In order to test a well with a permanent packer set inside a casing, a test string is required to be made up for running in the well. A test string typically includes, but is not limited to, the following components, in order, from the bottom up. A bullnose or wire-line re-entry guide, a packer seal assembly, a locator no-go, a tubing test valve, various testing and safety valves and tubulars of sufficient length to reach the set casing permanent packer. Because the permanent packer is pre-set and the packer forms part of the casing downhole, the test string length is determined by the following factors; tubing length and size--each length being individually measured, and the temperature and stretch of the tubing in the well. The test string length must correspond to the packer depth almost exactly.
To try and pre-calculate the amount of pipe required to exactly enter a permanent packer, and be correct within inches, is impossible in practice. The standard technique used is therefore to calculate the pipe requirement approximately, and then enter the packer bore until pipe will not enter any further. This is the point when the locator no-go abuts the top of the permanent packer and this can be detected on the drilling rig. From this known point and a second known point which is the location of the formation top surface, i.e. the sea bed or land surface, the complete test string can be spaced out as required. This is typically done by painting a section of pipe white and closing a set of pipe rams contained in the drilling BOP stack to give it an exact mark. Using this marking the pipe can be spaced out as necessary to include well test equipment such as a subsea test tree and other tools. During this space-out the string is run-in until the locator no-go abuts the top of the packer; the string is then withdrawn several feet, for example 10 feet from the packer, so that there is a good seal between the packer seal assembly and the interior surface of the packer called the polished bore receptacle (PBR). This packer seal assembly includes alternate bands of metal and elastomer, usually "VITON" (trademark) seals, so that slight movements relative to the PBR do not effect the seal in between the tool and the permanent packer.
Existing tubing test valves allow the mud/fluid contained within the casing to freely enter the test string as the test string is lowered downhole by adding each section/length of tubular. A typical tubing test valve currently used is the Halliburton TST (Tubing String Tester) valve which allows the DST string to be pressure tested while running in the hole. The Halliburton TST valve includes a flapper valve and spring so that when running in the hole the flapper valve opens and allows the test string to fill up. When the test string is stationary the flapper valve is held closed by the spring. The string can be pressure tested as many times as required while running in the hole. With valves of this type the tubulars can be internally tested by pumping down inside the test string on top of the tubing test valve. The pressure is monitored at the surface and pressure testing verifies the pressure integrity of the connections of the tubulars and assemblies above the tubing test valve. Therefore, the pressure test procedure can be repeated as many times as desired until all tubulars are added to give the full length of the test string. As described above, the full length of the test string is determined by the space out from the locator no-go. Once the full length of the string has been determined then various test tools can be added to the string as required in order to permit safe testing of the well.
Therefore, the procedure is to run-in to determine the length of tubulars and test equipment and during run-in the test valve is free to permit fluid passage, but when stationary the test valve is closed and must support pressure from above to pressure test the connections of tubulars and the like. Once the space out has been achieved and the location of the packer known, the test string must be partially retrieved where additional equipment is then fitted and the string run in again and the testing procedure can be repeated to check the integrity of the additional well test components.
Existing tubing test valves allow the seal assembly to enter the set packer by permitting fluid/pressure by-pass to the now engaged seals as they compress what may be a closed volume below the packer. The volume below the packer may be closed because the casing/formation has not been perforated or the formation may be sufficiently impermeable such that the volume is effectively closed. If the volume is closed, the tool may get stuck in the well because of the enormous hydraulic force created by trying to pull the engaged seals or the set packer against the closed volume below. In extreme cases this could result in equipment loss or in the well being abandoned.
One existing solution is to provide fluid by-pass communication between the exterior and interior of the tubing and require hydraulic actuation from annulus pressure.
In an alternative arrangement it is possible to run two test valves in series, for example, a Halliburton TST valve with a Halliburton LPN-NR formation tester valve beneath it. However, the LPR-NR valve does not allow self-filling and needs to be held open during run-in. However, use of the LPR formation tester valve in this application is out in this design mode and may compromise the operation of the tool during the mode downhole. In this regard, during initial run-in the LPR is held open and the TST permits self-filling to the string and pressure testing of the tubulars and components. After location of the no-go and proper space out, the TST has to be fired open. This means that to pressure test the well equipment, the LPR-N has to be closed. If the LPR fails it will automatically close and it may not be possible to by-pass the pressure between the closed formation and the interior of the tubing. This arrangement does not permit multiple re-entry of the tool or fluid by-pass.
An object of the present invention is to provide an improved tubing test valve which obviates or mitigates at least one of the aforementioned disadvantages.
A further object of the present invention is to provide a tubing test valve which permits multiple entry of the string to, and retrieval from, permanent packers without committing the tool to the locked open position.